Fix data race when moving a stream (#5880)

There was a data race that triggered in
`TestJetStreamSuperClusterMoveCancel` due to the addition of JetStream
asset version metadata.

All JS API requests receive user-provided
`StreamConfig`/`ConsumerConfig`, which ensures that any mutations done
in `setStaticStreamMetadata` for example is safe.

However, `jsLeaderServerStreamMoveRequest` and
`jsLeaderServerStreamCancelMoveRequest` would use the `sa.Config` from
the stream assignment and call into `jsClusteredStreamUpdateRequest`.
This resulted in a reference to the same `Metadata` map being available
and modified.

To ensure any changes made to config defaults or metadata doesn't result
in a data race, a `StreamConfig.clone` method is added.


[data-race-TestJetStreamSuperClusterMoveCancel.txt](https://github.com/user-attachments/files/16968281/data-race-TestJetStreamSuperClusterMoveCancel.txt)


Signed-off-by: Maurice van Veen <github@mauricevanveen.com>

---------

Signed-off-by: Maurice van Veen <github@mauricevanveen.com>

server/jetstream_api.go

@@ -2493,7 +2493,7 @@ func (s *Server) jsLeaderServerStreamMoveRequest(sub *subscription, c *client, _
 	if ok {
 		sa, ok := streams[streamName]
 		if ok {
-			cfg = *sa.Config
+			cfg = *sa.Config.clone()
 			streamFound = true
 			currPeers = sa.Group.Peers
 			currCluster = sa.Group.Cluster
@@ -2635,7 +2635,7 @@ func (s *Server) jsLeaderServerStreamCancelMoveRequest(sub *subscription, c *cli
 	if ok {
 		sa, ok := streams[streamName]
 		if ok {
-			cfg = *sa.Config
+			cfg = *sa.Config.clone()
 			streamFound = true
 			currPeers = sa.Group.Peers
 		}

server/jetstream_test.go

@@ -24329,3 +24329,38 @@ func TestJetStreamRateLimitHighStreamIngestDefaults(t *testing.T) {
 	require_Equal(t, stream.msgs.mlen, streamDefaultMaxQueueMsgs)
 	require_Equal(t, stream.msgs.msz, streamDefaultMaxQueueBytes)
 }
+
+func TestJetStreamStreamConfigClone(t *testing.T) {
+	cfg := &StreamConfig{
+		Name:             "name",
+		Placement:        &Placement{Cluster: "placement", Tags: []string{"tag"}},
+		Mirror:           &StreamSource{Name: "mirror"},
+		Sources:          []*StreamSource{&StreamSource{Name: "source"}},
+		SubjectTransform: &SubjectTransformConfig{Source: "source", Destination: "dest"},
+		RePublish:        &RePublish{Source: "source", Destination: "dest", HeadersOnly: false},
+		Metadata:         make(map[string]string),
+	}
+
+	// Copy should be complete.
+	clone := cfg.clone()
+	require_True(t, reflect.DeepEqual(cfg, clone))
+
+	// Changing fields should not update the original.
+	clone.Placement.Cluster = "diff"
+	require_False(t, reflect.DeepEqual(cfg.Placement, clone.Placement))
+
+	clone.Mirror.Name = "diff"
+	require_False(t, reflect.DeepEqual(cfg.Mirror, clone.Mirror))
+
+	clone.Sources[0].Name = "diff"
+	require_False(t, reflect.DeepEqual(cfg.Sources, clone.Sources))
+
+	clone.SubjectTransform.Source = "diff"
+	require_False(t, reflect.DeepEqual(cfg.SubjectTransform, clone.SubjectTransform))
+
+	clone.RePublish.Source = "diff"
+	require_False(t, reflect.DeepEqual(cfg.RePublish, clone.RePublish))
+
+	clone.Metadata["key"] = "value"
+	require_False(t, reflect.DeepEqual(cfg.Metadata, clone.Metadata))
+}

server/stream.go

@@ -104,6 +104,42 @@ type StreamConfig struct {
 	Metadata map[string]string `json:"metadata,omitempty"`
 }
 
+// clone performs a deep copy of the StreamConfig struct, returning a new clone with
+// all values copied.
+func (cfg *StreamConfig) clone() *StreamConfig {
+	clone := *cfg
+	if cfg.Placement != nil {
+		placement := *cfg.Placement
+		clone.Placement = &placement
+	}
+	if cfg.Mirror != nil {
+		mirror := *cfg.Mirror
+		clone.Mirror = &mirror
+	}
+	if len(cfg.Sources) > 0 {
+		clone.Sources = make([]*StreamSource, len(cfg.Sources))
+		for i, cfgSource := range cfg.Sources {
+			source := *cfgSource
+			clone.Sources[i] = &source
+		}
+	}
+	if cfg.SubjectTransform != nil {
+		transform := *cfg.SubjectTransform
+		clone.SubjectTransform = &transform
+	}
+	if cfg.RePublish != nil {
+		rePublish := *cfg.RePublish
+		clone.RePublish = &rePublish
+	}
+	if cfg.Metadata != nil {
+		clone.Metadata = make(map[string]string, len(cfg.Metadata))
+		for k, v := range cfg.Metadata {
+			clone.Metadata[k] = v
+		}
+	}
+	return &clone
+}
+
 type StreamConsumerLimits struct {
 	InactiveThreshold time.Duration `json:"inactive_threshold,omitempty"`
 	MaxAckPending     int           `json:"max_ack_pending,omitempty"`